Conventional motion picture film comprises frames that are commonly displayed sequentially at a frame rate of 24 frames per second (24 fps), or 30 fps, or some other rate. Required special effects may embodied in the displayed film.
Systems (including "telecine" systems) have been developed for converting motion picture film into video signals. These systems generate a video signal from motion picture film images by scanning the film frames sequentially to generate digitized film images. They then convert the digitized images into a video signal having a standard video frame rate (25 video frames per second for PAL video, 29.97 video frames per second for NTSC video, or 30 video frames per second for SMPTE-240M high definition video). Each video frame consists of two fields.
Conventional telecine systems are "real time" system in the sense that they generate a video signal from motion picture film images at a desired video frame rate (such as the standard PAL or NTSC video frame rate).
Due to the mismatch between the film frame rate (24 fps) and the PAL video frame rate (25 fps), motion picture film is often fed through a conventional PAL telecine system at the slightly elevated rate of 25 film frames per second, for the sake of processing convenience.
Due to the mismatch between the conventional film frame rate (24 fps) and the NTSC video frame rate (approximately 30 fps), a so-called "3-2 pulldown" (or "3-2-3-2 pulldown") technique is commonly employed to generate NTSC video using a telecine system. A version of such 3-2 pulldown technique will be described with reference to FIG. 7. Because the proposed SMPTE-240M standard for high definition digital video specifies a video frame rate of 30 frames per second, a 3-2 pulldown operation or its equivalent may also be useful to generate SMPTE-240M video using a telecine system.
The "real time" nature of conventional telecine systems gives rise to a number of disadvantages. Such systems can have a tendency to damage or break the film being processed due to the high speed at which the film is translated through the scanner and the way the film is handled. Also, the high processing rate of conventional telecine systems could require expensive and complicated circuitry for digitizing the scanned data with more than eight-bit quantization.
Until the present invention, no system has been developed for generating digitized color film images from motion picture film at a slow (less than real-time) rate, digitally correcting the digitized images at the same slow rate (or at a different slow rate), and digitally generating a video signal (having a standard frame rate) from the digitized images.
Throughout the specification, including in the claims, the phrase "slow rate" will be used to denote a less than real-time frame rate. For example, the invention may scan motion picture film (of the type that is normally displayed at a real-time rate of 24 fps) at a "slow rate" of 1.5 fps or 1.875 fps, and digitally perform color correction on the scanned data at another "slow rate" of 6.0 fps or 7.5 fps.
Also throughout the specification, including in the claims, the phrase "standard frame rate" will be used to denote a real-time frame rate. For example, the proposed standard frame rate of an SMPTE-240M digital video signal is 30 frames per second, and the standard frame rate of conventional motion picture film is 24 frames per second